Catheter placement device and method

ABSTRACT

A medical device for use in intravenous or intraarterial injections of fluids, in blood sampling, in diagnostic procedures such as intravascular blood sampling including sampling in the heart, and in intravascular pressure measurements using transducers. The device incorporates a novel catheter means and method for placing a flexible cannula in a vein or artery such that the catheter means can be threaded through the cannula into the vein or artery of a patient an appropriate distance. The catheter can be secured in position relative to the cannula by means of a self-contained locking arrangement carried by the catheter. In preferred forms, the locking force against the catheter can be distributed over an area to assure a good lock without restricting the catheter and without the expense of providing close tolerance in the locking system.

United States Patent 3,406,685 10/1968 May Inventors Appl. No. Filed Patented Assignee Ralph D. Alley Loudonville, N.Y.;

David S. Sheridan, Argyle, Wash. 843,866

Mar. 13, 1969 Jan. 1 l, 1972 Sherwood Medical Industries Inc. Continuation-impart of application Ser. No. 640,889, May 24, 1967, now abandoned. This application Mar. 13, 1969, Ser. No. 843,866

CATHETER PLACEMENT DEVICE AND METHOD 12 Claims, 14 Drawing Figs.

Primary Examiner Dalton L. Truluck An0rneyHofgren, Wegner, Allen, Stellman & McCord This application filed under Rule 47.

ABSTRACT: A medical device for use in intravenous or intraarterial injections of fluids, in blood sampling, in diagnostic procedures such as intravascular blood sampling including sampling in the heart, and in intravascular pressure measurements using transducers. The device incorporates a novel catheter means and method for placing a flexible cannula in a vein or artery such that the catheter means can be threaded through the cannula into the vein or artery of a patient an appropriate distance. The catheter can be secured in position relative to the cannula by means of a self-contained locking arrangement carried by the catheter. In preferred forms, the locking force against the catheter can be distributed over an area to assure a good lock without restricting the catheter and without the expense of providing close tolerance in the locking system.

PATENIEDJAIHBR 31633579 'SHEEI 1 OF 2 :"tilfi-I.

M2 58 4-8 '8 50 l E TORS NV N H66 RALPH 0. ALLEY DAVID S. SHERIDAN ATTORNEYS.

1 CATHETER PLACEMENT DEVICE AND METHOD RELATION TO COPENDING APPLICATION This application is a continuation-in-part of our copending application Ser. No. 640,889, filed May 24, 1967 and entitled Catheter Placement Device and Method, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in a catheter and method of placing same, and more particularly to an intravenous catheter placement unit and method.

2. Statement of the Prior Art A few short years ago intravenous catheters were placed by a doctor making a surgical incision or cutdown in the skin and vein so that the distal end of a catheter could be inserted directly into the vein and threaded a limited distance therein as desired. Recently, needle and catheter devices have been marketed which made it possible to place an intravenous catheter by using the needle portion of the device to penetrate the intact skin for the catheter. That is, during a medical procedure requiring the use of an intravenous catheter having a fitting on the proximal end thereofor having a funnel-shaped proximal end portion, difficulty has been experienced in disposing of the cannulated needle after the catheter has been placed. At least three methods have been known to have been used heretofore. The first method incorporates the use of a relatively large bore needle with a flexible catheter passing through said bore. The needle with the distal end of the catheter nested therein is first inserted into the vein of the patient whereupon the catheter is threaded through the needle into the vein an appropriate distance. The needle is then withdrawn from the wound, leaving the catheter in place. The needle, due to the fitting or funnel on the catheter, cannot be removed from the catheter and because of its stiffness and its sharp point must now be secured to the patient and to the catheter in such a way as to prevent the needle from rupturing the catheter or from further puncturing the arm ofthe patient. This last-mentioned procedure wastes considerable length of catheter and requires an additional encumbrance to the patient where the needle is taped down to protect the catheter. Another disadvantage of this system lies in the fact that once the needle is removed from the vein, it becomes almost impossible to advance the catheter further.

Another disadvantage of this system is that the catheter has to be threaded through the needle while the needle is in position in the vein of the patient. During the medical procedures requiring the use of intravenous catheters it is often necessary to manipulate the catheter in and out of the vein to pass the distal end past an obstruction in the vein. Using the needle as the guiding means for the catheter into the vein, any backward movement on the catheter causes the heel on the beveled needle to cut into the catheter and has been known to completely sever the catheter so that the severed portion will float freely in the vein of the patient creating medical complications. In addition, if the patient should move or flex the portion of the body where the needle has been inserted, it could cause the needle to damage the inside wall of the vein or to even puncture another opening in the vein.

In another prior method a needle is nested on the inside ofa flexible catheter with the point of the needle extending forwardly of the catheter. The combined catheter and needle is inserted into the patient and the needle is then removed from the inside of the catheter so as to leave the catheter in place in the vein. A connection is made to the proximal portion of the catheter so as to extract blood or inject fluids into the bloodstream. Using this system, if it is desired to place a long catheter in the vein of the patient, it is necessary to have an equally long needle passing up the inside thereof. It is obviously impractical to have needles 150 cm. long and even longer since they become excessively flexible, difficult to manipulate, and since the needle cannot bend around turns or the like in the vein, they cannot be placed beyond the first turn.

A third prior method provides a cannulated needle about the outer surface of the catheter, which needle is split longitudinally such that when the needle is removed from the patient, the needle can be peeled back, removed from the catheter and discarded. This has eliminated the problem of protecting the catheter from the needle once the needle is removed from the patient, but difficulty in finding materials stiff enough for use as a needle and still pliable enough to be removed from the catheter as intended has been a problem. Secondly, once the needle is removed, no means for changing position of the catheter is available.

SUMMARY OF THE INVENTION AND EXEMPLARY USES The present invention, to the extent described in our aboveidentified copending patent application and also described herein, overcomes the disadvantages of the prior art and provides for a flexible cannula having a needle or stylet through the center bore thereof with the point extending beyond the exposed end of a cannula. The combined cannula and needle is inserted through the skin and into the vein of a patient. The needle is then withdrawn and the cannula is permitted to maintain its position in through the skin and into the vein of the patient. A long flexible catheter of matching size or of a smaller diameter is then inserted into the flexible cannula and is threaded through the cannula into the vein of the patient an appropriate distance. A locking system is provided for locking the catheter relative to the cannula in position in the vein. Any one of the well-known medical fittings is provided on the proximal end of the catheter which makes it possible to connect the catheter to selected equipment for either injecting fluids into or for removing fluids from the patient. The catheter can be unlocked from the cannula and can then be either inserted further, manipulated, or withdrawn in whole or in part from the cannula. The cannula can remain in position in the patient and when no catheter is in position therein, its proximal end is capped or sealed.

With the cannula in place in the patient, the doctor is free to employ any one of many different catheters or diagnostic devices. For instance, by way of example but not limited thereto, long or short length catheters can be interchanged, different diametered catheters up to the limit of the inside diameter of the cannula can be used, catheters with different radio opacities such as X-ray opaque lines or completely X- ray opaque, can be employed, and catheters of different tip configurations can be substituted. The required catheter is selected and is threaded through the cannula into the patient as soon as the cannula is uncapped. The locking system is adapted to lock the catheter to the cannula at the required point, said locking system also serving as a sealing means for preventing blood from flowing between the catheter and cannula.

Although the device of this invention has been found to function in an excellent manner, in a further and preferred aspect of the invention we have now further improved the locking system especially where the locking system includes means resiliently urging against the outer surface of the catheter. Using the further improvement, the resilient force can be distributed or dissipated over a larger area of the catheter outer surface so that tolerances in manufacture of the locking system need not be close. Further, the preferred locking system is easier and more surely moved to a locking and sealing relationship with the catheter and minimizes forces which might tend to slightly restrict the catheter.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawing and will be described in detail a specific embodiment of the invention together with modifications thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment or modifications illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a catheter placement device incorporating the principles of our invention;

FIG. 2 shows a cannula and needle of our device in position in a vein or artery of a patient;

FIG. 3 shows the cannula of FIG. 2 in position in the patient with the needle removed;

FIG. 4 shows the cannula of FIG. 3 in position in the patient with a portion of a catheter threaded through a ferrule and through the cannula;

FIG. 5 shows the cannula and catheter in position with the ferrule locking the catheter relative to the cannula;

FIG. 6 is a cross-sectional view taken along the lines 6-6 of FIG. 5;

FIG. 7 is a cross-sectional view taken along the lines 7-7 of FIG. 6;

FIG. 8 is a cross-sectional view taken along the lines 8-8 of FIG. 6;

FIG. 9 is an enlarged partial cross-sectional view similar to a portion of FIG. 6 only employing a different diametered catheter;

FIG. 10 is a cross section showing an improved locking system in locking and sealing position;

FIG. 11 is a fragmentary view of a locking member of the system of FIG. 10;

FIGS. 12 and 13 are fragmentary views of other forms of locking members which may be used in the same general manner as the locking member in FIGS. 10 and I1; and

FIG. 14 is a fragmentary view from the top of the locking member as illustrated in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 through 9, one embodiment of the invention is illustrated in substantially full scale view except certain cross-sectional views are enlarged to help illustrate the principle of the invention.

The embodiment of the invention shown in FIG. 1 comprises a needle 10 and a cannula 12 combined as one unit 14. A catheter l6 and locking member or ferrule 18 is combined as a second unit 20. The needle 10 can either be in the form of a stylet or a hollow needle with either a pencil point (not shown) on the end thereof or a tapered point 22, as desired. The tapered point 22 of the stylet or needle 10 extends from sharp point gradually sloping to a junction with the opposite wall of the needle. The point of the needle in the illustrated form extends beyond the forward portion of the cannula 12. The proximal end 26 of the needle is connected with a cylindrical connector member 28 which has a knurled portion 30 on its outer surface for gripping purposes. In the illustrated form of needle 10, it is hollow and will permit fluids to flow through the bore therein.

The cannula 12 is formed of a plastic material that is flexible enough to flex and bend into conforming shapes without too much effort and is still stiff enough to adhere to the needle and be pushed through an incision made by the needle point into the vein of the patient. The material of the cannula should also be stiff enough to withstand collapsing forces created by the skin and tissues of the patient against the cannula when the needle is removed and the cannula is in unsupported condition in the patient.

The cannula 12 has an elongate portion 32 of uniform diameter conforming to the outside diameter of the body of the needle. At the distal end of the portion 32 a taper 34 is fonned sloping downward to a feather edge 36. An enlarged section 38 is integrally formed on the proximal portion of the cannula and has an inner surface 40 tapering gradually from the proximal end down to the elongate portion 32. The cannula 12 encircles the needle 10 with the proximal end abutting against the cylindrical connector member 28 of the needle and with the feather edge 36 positioned either in alignment with the rear edge of the point bevel 22 or spaced in close proximity therewith.

The unit 20 including the catheter l6 and locking member or ferrule 18 is supplied as a separate item from the needle and cannula unit 14 although they are part of the same set. The catheter 16 may be of any desired length varying from 15 cm. to cm. and may be extruded from clear polypropylene or polyethylene material. The distal end 42 of the catheter may be provided with a single opening or may be a rounded blind end with plural openings 44 spaced down either side thereof. The major portion of the catheter 16 is composed of a substantially uniform-diametered body portion 45. An X-ray opaque line 46 may be embedded in said body portion and may run from the distal end 42 the full length of the catheter to the proximal end 48 or the line 46 can terminate at some intermediate point short of the proximal end. Spaced from the distal end portion 42 the body portion 45 of the catheter is gradually enlarged as at 50 and has an attaching means 52 carried on the proximal end 48 thereof. The attaching means 52 could be for use with a Luer lock arrangement or any other appropriate attaching device. The gradually tapering portion 50 of the catheter has an external surface lying at a predetermined shallow angle relative to the axis of the catheter for a purpose to be described hereinafter. The catheter can be made of an X-ray opaque material such that it will permit visual placement of the catheter under fluoroscope.

The locking member or ferrule 18 has a tapered body portion 54 extending from a wide mouthed proximal end 56 to a narrow-mouthed distal end 58. The opening at the distal end 58 is of a size approximating the outside diameter of the body portion 45 of the catheter so as to permit sliding relationship with the elongate body portion of said catheter. The outer sloping surface of the ferrule 18 lies at an angle relative to the axis of the ferrule which is slightly less than the angle of slope of the inside surface 40 of the enlarged portion 38 of the cannula 12. The inner surface of the ferrule 18 parallel to the axis of said ferrule has an angle which is slightly larger than the angle of slope of the exterior surface of the proximal end portion 50 of the catheter.

The ferrule or locking member 18 should be made of a material such as polyvinyl which is softer than the material of the catheter so that when it is desired to lock the catheter relative to the cannula, the locking member or ferrule I8 is moved along the catheter until the distal end portion end portion 58 wedges between the slope 40 in the cannula and the outer surface of the body portion 45 of the catheter. The wedging ac tion will cause the distal end 58 of the ferrule to constrict and grip the outer surface of the catheter to lock the catheter against axial movement relative to the cannula. The gripping action will be such as not to constrict the catheter or to reduce its internal diameter in the vicinity of the locking contact. To release the lock between the cannula and catheter, the ferrule is twisted and urged toward the proximal end of the catheter until it releases the locking action whereupon the ferrule can be moved along the length of the catheter and the catheter can be moved in or out relative to the cannula.

As shown in FIG. 2, a section of the anatomy of a patient is shown cut away illustrating a portion of skin 60 with a vein below the skin identified as 62. The needle and cannula unit 14 is assembled on the hub of a syringe or other manipulating instrument such that the needle is used to puncture the skin and one wall of the vein for placing the cannula in the vein. Once the point 22 of the needle 10 punctures the vein, blood will flow up the hollow portion of the needle so that the person placing the cannula can tell that the vein has been pierced. The needle 10 can now be removed from the cannula l2 and the proximal portion 38 of the cannula can be capped with an appropriate seal to prevent bleeding through the cannula. After removing the cap, the distal end 42 of the catheter 16 can be inserted through the cannula and can be carefully threaded into the vein of the patient. With very careful placement techniques the distal end of a catheter can be threaded through the vein and/or artery for a considerable distance, even all the way to the heart under certain circumstances.

Once the distal end of the catheter is positioned where desired, the locking member or ferrule 18 is slid along the body portion 45 of the catheter 16 until the distal end 56 of the ferrule 18 enters the proximal opening in the rear of the cannula. The ferrule 18 is forced into the sloping end of the cannula so that the distal end portion of the ferrule wedges between the sloping wall 40 of the cannula and the outer surface of the catheter. The pressure created by the wall 40 of the cannula against the outer forward surface of the distal end of the ferrule will cause the ferrule to grip the outer surface of the catheter and lock the catheter relative to the cannula. The gripping action is such as not to collapse the wall of the catheter but merely grips against the outer surface of the catheter without affecting the internal diameter of the catheter. The proximal end portion 52 of the catheter is then connected with the appropriate equipment for either injecting intravenous fluids into the vein of the patient or for whatever purpose the catheter has been placed.

FIGS. 6, 7, 8 and 9 illustrate the locking action created by the ferrule on the outer surface of the catheter and on the inner surface of the cannula FIG. 6 illustrates a catheter with an outside diameter substantially coinciding with the inside diameter of the cannula while FIG. 9 shows a catheter with an outside diameter considerably smaller than the inside diameter of the cannula. The forward or distal end portion 58 of the ferrule 18 first engages with the sloping wall 40 of the cannula which causes the circumference of the ferrule to constrict slightly against the outer wall surface of the catheter. This provides the gripping action between the ferrule and catheter for preventing the catheter from moving in or out relative to the ferrule. Since the ferrule on its outer surface of the distal end thereof is gripped against the slope of the cannula, it likewise cannot move and therefore the catheter is locked relative to the cannula. If it is decided that the catheter should be moved over or inserted in a greater distance in the vein, it is merely necessary to slightly twist and pull rearward on the ferrule until it is unseated from the cannula whereupon the catheter may be further slid or threaded through the cannula into the vein of the patient an appropriate distance.

In FIG. 9 the catheter 16' has an outside diameter which is smaller than the inside diameter of the cannula 12. The ferrule 18 has its distal end opening of an inside diameter coinciding with the outside diameter of the catheter 16. The end 58 of the ferrule is adapted to engage the inner surface of the cannula to constrict the opening in the ferrule sufficient to grip and lock the catheter relative to the cannula. It is recognized that blood can flow between the catheter and the cannula but the ferrule will serve as a plug to block any bleeding around the catheter beyond the distal end of the ferrule. As a practical matter only a few drops of blood would be permitted to seep between the catheter and ferrule.

The last enumerated feature, namely, the ability to use different diametered catheters up to a maximum equal to the inside diameter of the cannula lends considerable flexibility to the device. Frequently, after the cannula of a certain size is set in place, it is desired to insert different catheters for different purposes, each catheter possibly being of a different diameter or different characteristic, i.e., X-ray opaque, blunt or openended and the like. The ability to use the same cannula for various diagnostic and treatment devices while still being able to lock the catheter in a desired position is an important and useful element of our invention.

The herein disclosed catheter placement device makes it possible to have the needle which is used to assist in the placement of the cannula in the vein completely removed from the device so as not to create the usual hazards incident to having the needle on the catheter during use of the device. It is contemplated that a packaging means will be provided with the catheter and ferrule unit such that the catheter could be threaded through the cannula directly from a sterile package without the doctor or technician actually touching the outer surface of the catheter.

The method of placing the catheter becomes quite simple when the technique has been mastered. That is, the needle and cannula unit 14 is removed from its sterile package and is inserted through the skin and into the vein of a patient. Blood coming up the needle will indicate when the needle and cannula are in proper position. The needle is then removed from the cannula, plugged by plug 39, an the cannula is taped to the skin of the patient. Immediately prior to entry of the appropriate catheter into the cannula, the plug 39 is removed from the cannula, and placed on the proximal end of the catheter. Now the catheter with the ferrule surrounding the body thereof is then threaded carefully through the cannula until the distal end of the catheter reaches the appropriate location in the patient. The ferrule is then slid forward on the catheter and locks the catheter relative to the cannula. The proximal end portion of the catheter is then attached to the appropriate mechanism for intravenous feeding or whatever other purpose the catheter has been placed.

The device makes it possible to require only one vein puncture such that the catheter or different catheters may be inserted through the cannula as many times as is desired. Once the needle and cannula have entered the lumen of a vein, the needle is removed and the cannula taped in position for an indefinite period of time, for instance, up to 3 weeks. The proximal end of the cannula may be plugged when no catheter is in position so as to prevent bleeding up the cannula. Since the cannula is of plastic material, it does not present sharp edges in the lumen of the vein and therefore there is no danger that movement of the patient in the vicinity of the cannula will cause the cannula to puncture the walls of the vein or the skin of the patient.

Turning now to FIGS. 10, 11 and 14, the locking system shown is similar to that shown in FIG. 9 except that ferrule 18a has a tapered distal end 58a. When the ferrule 18a is moved to locking position tightly engaging the outer surface of catheter 16, the force against the outer surface is distributed over larger elliptical area rather than a smaller circular area and the inner surface of the ferrule 18a near end 58a is permitted to flatten out more between the cannula inner surface and the catheter outer surface for better sealing at less close fitting tolerances. Also, the pointed end pivoted by the taper assists in assembly of the device and movement of the ferrule 18a to its locking and sealing position. The wide area of contact produces a better lock without crushing or constricting the catheter.

In FIG. 12, a slit 59 at ends 58b provides a similar function in increasing the area of engagement, distributing force, decreasing the closeness of tolerances required and providing a better and more positive seal. More than one slit 59 may be employed so as to provide a greater tolerance level between inside of the cannula and the outside diameter of the catheter. In making the slits some material is removed so that the diameter of the outer end 58b can be reduced by pressing the slit or slits 59 closed. This permits the greater tolerance between the cannula and the catheter and distributes the contact surface therebetween over a wider area. In addition the slit intersection with the end 58b provides longitudinal edges 60, 61 which serve to grip the inner surface of the cannula and the outer surface of the catheter in a more positive manner. That is, as the ferrule is pushed into the cannula for locking it is twisted relative thereto and as a result either edge 60 or 61 will bite into the cannula and catheter to increase the gripping and locking action.

In FIG. 13, end 580 of ferrule 18c is provided with a circular bevel eliminating the outer square circular edge of ferrule 18 and, in effect, defining an inwardly tapered frustoconical end 64. The tapered end 64 has two lines or rings 65, 66 of contact which are spaced axially apart by the amount of taper in the end 64. As the ferrule is pushed into the cannula and twisted for locking purposes, the ring 66 will apply force to the cannula and the ring 65 will apply force to the catheter. As the locking forces increase the areas around the rings 66, 65 will assume some of the locking forces to provide a more positive lock to the catheter relative to the cannula. It will be apparent that end 580 permits easier movement of ferrule 18c to locking position and that the end, being progressively less thick, will deform over a larger area between the outer surface of catheter 16 and the cannula l2 and provide a more complete force distributing seal even when the parts are made to wider manufacturing tolerances.

Other modifications, uses and advantages of this invention will be evident to those skilled in the art.

We claim:

1. in a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having a tapered distal end portion and a flared proximal end portion and locking means comprising a ferrule slidably carried on said catheter for locking said catheter relative to said cannula when said catheter is in position in said cannula, said ferrule having a tapered outer wall and a continuous inner wall, the distal end of said ferrule engaging with the inner surface of the tapered distal end portion of the cannula for creating the locking action against the outer surface of said catheter.

2. A device as claimed in claim 1 wherein said catheter is made of a plastic material and has an Xray opaque line extending from the distal end through at least a portion of said catheter.

3. A device as claimed in claim 1 wherein said catheter is made of an X-ray opaque material.

4. A device as claimed in claim 1 wherein means are provided on the proximal end of said catheter for attaching said catheter to another instrument.

5. The device of claim 1 wherein at least the distal end portion of said ferrule is flexible.

6. The device of claim 1 wherein said locking action comprises means for distributing the force against the catheter over a portion of the length of said catheter.

7. The device of claim 6 wherein the force spreading means comprises a frustoconical end on said ferrule engaging said catheter.

8. The device of claim 6 wherein the force spreading means comprises slit means in the wall of said ferrule extending axially from the catheter engaging end thereof.

9. in a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having an enlarged proximal end portion with a tapered inner wall surface therein, locking ferrule means slidably carried on said catheter in a position proximally located with respect to said enlarged end of said cannula, said ferrule having an outer wall surface tapered downwardly toward the distal end thereof, said distal end of said ferrule being wedged between the inner tapered wall of said cannula and the outer surface of said catheter for locking said catheter relative to said cannula.

10. A method of placing a catheter in a patient comprising the steps of inserting a cannula shrouded needle into a body cavity of a patient, withdrawing the needle from the cannula and leaving the cannula in position in the patient, sliding a locking ferrule that surrounds an elongate thin flexible catheter toward the proximal end of said catheter so as to expose a length of catheter forward of said ferrule, threading said catheter through said cannula into position in said pa tient, and locking said catheter relative to said cannula by wedging said ferrule between said cannula and the outer surface of said catheter.

11. in a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having an enlarged proximal end portion with a tapered inner wall surface therein, and locking means comprising a ferrule slidably carried on said catheter for locking said catheter relative to said cannula when said catheter is in position in said cannula, said ferrule having a tapered outer wall and a continuous inner wall, the distal end of said ferrule being wedged between the inner tapered wall of said cannula and the outer surface of said catheter for locking said catheter relative to said cannula.

12. A method of placing and securing a catheter in a patient comprising the steps of inserting a cannula shrouded needle into a vein or artery of a patient, withdrawing the needle from the cannula and leaving the cannula in position in the patient, positioning a locking ferrule over the distal end of the catheter with the locking end of said ferrule pointed toward said distal end, sliding said ferrule toward the proximal end of said catheter, threading the distal end of said catheter through said cannula into position in said patient, and locking said catheter relative to said cannula by wedging said distal end of said ferrule between said cannula and the outer surface of said catheter. 

1. In a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having a tapered distal end portion and a flared proximal end portion and locking means comprising a ferrule slidably carried on said catheter for locking said catheter relative to said cannula when said catheter is in position in said cannula, said ferrule having a tapered outer wall and a continuous inner wall, the distal end of said ferrule engaging with the inner surface of the tapered distal end portion of the cannula for creating the locking action against the outer surface of said catheter.
 2. A device as claimed in claim 1 wherein said catheter is made of a plastic material and has an X-ray opaque line extending from the distal end through at least a portion of said catheter.
 3. A device as claimed in claim 1 wherein said cAtheter is made of an X-ray opaque material.
 4. A device as claimed in claim 1 wherein means are provided on the proximal end of said catheter for attaching said catheter to another instrument.
 5. The device of claim 1 wherein at least the distal end portion of said ferrule is flexible.
 6. The device of claim 1 wherein said locking action comprises means for distributing the force against the catheter over a portion of the length of said catheter.
 7. The device of claim 6 wherein the force spreading means comprises a frustoconical end on said ferrule engaging said catheter.
 8. The device of claim 6 wherein the force spreading means comprises slit means in the wall of said ferrule extending axially from the catheter engaging end thereof.
 9. In a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having an enlarged proximal end portion with a tapered inner wall surface therein, locking ferrule means slidably carried on said catheter in a position proximally located with respect to said enlarged end of said cannula, said ferrule having an outer wall surface tapered downwardly toward the distal end thereof, said distal end of said ferrule being wedged between the inner tapered wall of said cannula and the outer surface of said catheter for locking said catheter relative to said cannula.
 10. A method of placing a catheter in a patient comprising the steps of inserting a cannula shrouded needle into a body cavity of a patient, withdrawing the needle from the cannula and leaving the cannula in position in the patient, sliding a locking ferrule that surrounds an elongate thin flexible catheter toward the proximal end of said catheter so as to expose a length of catheter forward of said ferrule, threading said catheter through said cannula into position in said patient, and locking said catheter relative to said cannula by wedging said ferrule between said cannula and the outer surface of said catheter.
 11. In a catheter placement device comprising a flexible plastic cannula, an elongate catheter threaded into said cannula, said cannula having an enlarged proximal end portion with a tapered inner wall surface therein, and locking means comprising a ferrule slidably carried on said catheter for locking said catheter relative to said cannula when said catheter is in position in said cannula, said ferrule having a tapered outer wall and a continuous inner wall, the distal end of said ferrule being wedged between the inner tapered wall of said cannula and the outer surface of said catheter for locking said catheter relative to said cannula.
 12. A method of placing and securing a catheter in a patient comprising the steps of inserting a cannula shrouded needle into a vein or artery of a patient, withdrawing the needle from the cannula and leaving the cannula in position in the patient, positioning a locking ferrule over the distal end of the catheter with the locking end of said ferrule pointed toward said distal end, sliding said ferrule toward the proximal end of said catheter, threading the distal end of said catheter through said cannula into position in said patient, and locking said catheter relative to said cannula by wedging said distal end of said ferrule between said cannula and the outer surface of said catheter. 